1. Field of the Invention
The present invention relates to a slide fastener for use in opening and closing an article such as a bag and clothes, and more particularly, to a curved slide fastener whose fastener tape is curved at a predetermined curvature in the horizontal direction with respect to a tape surface thereof.
2. Description of the Related Art
As a slide fastener to be attached to open and close an opening portion of a bag, the front of clothes and fly of trousers, a curved slide fastener in which a fastener tape thereof is curved at a predetermined curvature in the horizontal direction with respect to the tape surface thereof is sometimes used. In such a curved slide fastener, usually, a fastener tape is woven or knitted continuously into a linear shape and cut to a predetermined length, followed by deformation into a curved shape.
Generally, in weaving or knitting a tape such that it is curved at a predetermined curvature, plural warp yarns running linearly in parallel in a weaving direction or a knitting direction are poor in elasticity, so that only by adjusting yarn tension to be applied in the weaving direction or the knitting direction, the tape cannot be curved horizontally with respect to the tape surface. Further, even if a warp yarn having an elasticity is used, not only tension control is complicated but also complicatedness in various maintenances is induced, thereby disabling effective manufacturing of such a fastener.
A curved slide fastener whose fastener tape is deformed into the curved shape as described above has been disclosed in U.S. Pat. No. 3,003,212. The curved slide fastener disclosed in U.S. Pat. No. 3,003,212 is composed of a pair of opposing herringbone weaves. Of first and second fastener tapes different in length, in the longer first fastener tape, a shorter cord (core thread) than the length of the fastener tape is sewed along a fastener element attaching edge portion thereof, while in the shorter second fastener tape opposing the first fastener element attaching edge portion, a longer cord (core thread) than the length of the fastener tape is sewed along a fastener element attaching edge portion thereof. With this configuration, when element rows attached to the respective fastener element attaching edge portions are engaged, the fastener tape is curved in a single direction. Further, it is permissible to attach a shorter cord or belt than the length of the second fastener tape along the side edge portion of the second fastener tape on the side in which no cord is sewed.
On the other hand, Japanese Patent Publication No. 7-59205 has disclosed that solvent swellable synthetic fibers, for example, polyurethane fibers are woven or knitted into fastener tapes, and when a solvent is applied only to the one fastener tape, polyurethane fibers of the one fastener tape are swollen so that only the one fastener tape is expanded in the warp direction, thereby reshaping a slide fastener into a curved form. Further Japanese Patent Publication No. 7-59205 has disclosed fixing of the curved form by applying a hot melting type adhesive agent to the fastener tape after the slide fastener is reshaped into a curved form.
Although the aforementioned curved slide fasteners disclosed in U.S. Pat. No. 3,003,212 and Japanese Patent Publication No. 7-59205 have such an advantage that the curved shape of the fastener tape is always maintained stably, each of them has the following disadvantages.
In the curved slide fastener described in U.S. Pat. No. 3,003,212, the longer cord (core thread) than the fastener tape or the shorter cord than the fastener tape is attached along the fastener element attaching edge or its opposite side edge. Thus, it comes that the fastener tape is elongated or contracted forcibly to cope with the length of the cord. For this reason, even a fastener tape with a herringbone weave, there is a problem that wrinkle or wavy uneven surface occurs on the tape surface other than the portion on which the cord is attached. Moreover, if the cord or belt is sewed to not only a fastener element attaching edge portion but also an opposite side edge portion, the number of parts increases and further processing steps increase, which is disadvantageous economically or in terms of working efficiency.
Because the curved slide fastener described in Japanese Patent Publication No. 7-59205 described above is swollen by applying a solvent to the solvent swellable fibers of the one fastener tape so as to elongate the fastener tape in the warp direction to reshape the curved configuration, the degree of swelling needs to be controlled appropriately such that the solvent swellable fibers are swollen by a predetermined amount. However, the degree of the swelling is likely to change depending on the working environment, the physical property of the solvent swellable fibers, the amount of the solvent applied, and the like. Therefore, it is difficult to obtain a curved slide fastener which is curved at a predetermined curvature.